With the development of display technology, the flat panel device, such as Liquid Crystal Display (LCD) possesses advantages of high image quality, power saving, thin body and wide application scope. Thus, it has been widely applied in various consumer electrical products, such as mobile phone, television, personal digital assistant, digital camera, notebook, laptop, and becomes the major display device.
Most of the liquid crystal displays on the present market are back light type liquid crystal displays, which comprise a liquid crystal display panel and a back light module. The working principle of the liquid crystal display panel is to locate liquid crystal molecules between two parallel glass substrates, and a plurality of vertical and horizontal tiny electrical wires are between the two glass substrates. The light of back light module is reflected to generate images by applying driving voltages to control whether the liquid crystal molecules to be changed directions.
Generally, the liquid crystal display panel comprises a CF (Color Filter) substrate, a TFT (Thin Film Transistor) substrate, a LC (Liquid Crystal) sandwiched between the CF substrate and the TFT substrate and sealant.
There is one layer of thin film material on the CF substrate and the TFT substrate of the TN (Twisted nematic) type or STN (Super twisted nematic) type liquid crystal display panel, which mainly makes the liquid crystal molecules to be aligned in a certain direction, and is so called the alignment film. Generally, the material of the alignment film is polyimide (PI) material, comprising the rubbing alignment type PI material or the light alignment type PI material. However, either of the alignment materials has the drawback itself. First, the rubbing alignment type PI material can easily causes issues of powder particles, residual electrostatic and brush marks to reduce the process yield. Although the light alignment type PI material can avoid these problems, with the restriction of the material properties, the heat resistance and the aging resistance are poor, and meanwhile, the LC anchoring ability is weaker, and the quality of the panel is lowered; second, the PI material itself has high polarity and high water absorption. The storage and the delivery can easily change the property to result in the nonuniform alignment, and the price of the PI material is expensive, and the film formation process on the TFT-LCD is more complicated, which leads to the increase of the panel cost.
At present, the common VA (Vertical Alignment) type display panel is the PSVA (Polymer stabilized vertical alignment) mode. The liquid crystal display panel of this mode needs to add one or few kinds of polymeric monomers in the liquid crystal material, and to be irradiated with the ultraviolet light to make the polyreaction take place to form the protruding objects guiding the direction of the liquid crystal to be deposited on the substrate surface, which is beneficial for the liquid crystal to have specific Pre-angle for implementing orientation and alignment as driving liquid crystal. However, the issue of this technology is that the problems of uniformity, residual quantity of this polymeric monomer will influence the quality of the panel; meanwhile, in this PSVA type liquid crystal display panel, it is also required to implement processes of exposure, development, etching to the ITO at the TFT side for generating the pattern of fish bond, and the process is complicated; besides, the polymeric monomers in the PSVA type liquid crystal display panel requires two times of ultraviolet (UV) light irradiation to accomplish the polymerization, and the production cost is higher.